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Chapter 2

CHAPTER 2 NOTES - Evolutionary Psych

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PSYC 3420
Irwin Silverman

CHAPTER 2: THE SCIENCE OF EVOLUTIONARY PSCYHOLOGY • Evolutionary psychologist Karl Grammar formed a team of researchers to study sexual signals as they occur in a seminal context: singles bars • He stationed one set of observers inside the bars and used specially designed rating forms to record observations of how often women were touched by men at the bar • A different member of the research team approached each woman as she left the bar and asked whether she would be part of the study • Woman participants were photographed and completed a brief questionnaire about their use of birth control and the current point in their menstrual cycle • Grammar then digitalized the photographic images and used a computer program to calculate the proportion of skin each woman revealed • Women who were not taking oral contraceptives, men in the singles bar were far more likely to initiate touching with women who were at the most fertile time of their cycle - around the time of their ovulation • Woman who were not ovulating, in contrast, were touched less • So men might be able to detect subtle cues to when women are ovulating • Ovulating women also displayed more sexual signals via their clothing • Rather, ovulating women might be actively sending sexual signals - an interpretation that’s supported by another study that found that ovulating women initiate sexual encounters more than women at other phases of the cycle • Two features of the science of evolutionary psychology: a. Discovering previously unsuspected links between features of human reproductive biology and manifest behaviour b. Thinking about adaptive function THE ORIGINS OF HUMAN NATURE THREE THEORIES OF THE ORIGINS OF COMPLEX ADAPTIVE MECHANISMS • Three major theories proposed to account for the origins of adaptation: 1. Creationism or "intelligent design • The idea that a supreme deity created all of the plants and animals, from the largest whales to the smallest plankton in the ocean, from the simple single-celled amoebas to the complex human brain • It is not viewed as scientific theory for three reasons: i. It cannot be tested ii. It has not guided researchers to any new scientific discoveries iii. It has not proved useful as a scientific explanation for already discovered organic mechanisms • Creationism is a matter of religion and belief, not a matter of science 2. Seeding theory • Life did not originate on Earth • Two versions of this theory: i. The seeds of life arrived on Earth via a meteorite ii. Extraterrestrial intelligent beings came down from other planets/galaxies and planted seeds of life on Earth CHAPTER 2 page 1 • These seeds eventually evolved into humans and other life forms • Seeding theory is in principle testable • Three problems of the seeding theory: i. There is currently no solid scientific evidence on earth that such "seedings" have taken place ii. It has not led to any new scientific discoveries nor has it explained any existing scientific puzzles iii. It simply pushes the causal explanation for life forms back in time 2. Evolution by natural selection • The many virtues of this theory: i. It explains known facts ii. It leads to new predictions iii. It provides guidance to important domains of scientific inquiry • It is the only known scientific theory that can explain diversity of life • There is no real contrast between all these three theories THE THREE PRODUCTS OF EVOLUTION • The three products of evolutionary theory: 1. Adaptations • Inherited and reliably developing characteristic that came into existence through natural selection because it helped to solve a problem of survival or reproduction during the period of it evolution • Ex. Umbilical cord • An adaptation must have genes "for" that adaptation • An adaptation must develop reliably among species members in all "normal" environments • Most adaptations are species-typical • Standards for evaluating a hypothesized function of an adaptation typically include:  Efficiency  Precision  Reliability • The environment of evolutionary adaptedness (EEA), refers to the statistical composite of selection pressures that occurred during an adaptation's period of evolution responsible for producing the adaptation  Ex. The EEA of the eye, refers to the specific selection pressures that fashioned each of the components of the visual system over 100 million years ago  The EEA doesn't refer to a SPECIFIC time or place, but rather to the SELECTION OF FORCES that are responsible for shaping adaptations • The adaptations period of evolution refers to the time span during which it was constructed, piece by piece, until it came to characterise the universal design of the pieces 2. By-products of adaptation (or concomitants) • Characteristics that do not solve adaptive problems and do not have functional design CHAPTER 2 page 2 • They are "carried along" with characteristics that do have a functional design because they happen to be coupled with those adaptations • Ex. Belly button - it is a by-product of something that was an adaptation, such as the umbilical cord 3. Random effects (or noise) • Random effects produced by forces such as chance mutations, sudden and unprecedented changes in the environment, or chance effects during development • Ex. Particular shape of a person's belly button • Despite scientific quibbles about the relative size of the three categories of evolutionary products, all evolutionary scientists agree on one fundamental point: adaptations are the primary product of evolution by selection • The core of all animal natures, including humans, consists of a large collection of adaptations LEVELS OF EVOLUTIONARYANALYSIS IN EVOLUTIONARY PSYCHOLOGY The hierarchy of levels of analysis in evolutionary psychology: GENERAL EVOLUTIONARY THEORY • "Evolution by natural selection" • Evolution by natural selection is understood from the "gene's eye" perspective - differential gene replication is the engine of the evolutionary process by which adaptations are formed MIDDLE-LEVEL EVOLUTIONARY THEORIES 1. Theory of Parasite-Host Coevolution 1. Theory of Parental Investment and Sexual Selection o Triver's theory - the sex that invests more resources in its offspring (often, but not always, females) will evolve to be more choosy or discriminating in selecting a mate o It is not "maleness" or "femaleness" itself that causes the sex difference in choosiness; rather, it is the relative parental investment of the two sexes o Ex. Unlike many species the female of Mormon cricket is larger, stronger, and more aggressive - therefore, the does more parental investment, and so females are selected for the size and other qualities that lead to success in competition with other females • Hypothesis 1: in species which the sexes differ in parental investment, the higher investing sex will be more selective in choice of mating partners  This is an psychological hypothesis because it proposes the existence of a specific psychological mechanism - a desire - that is designed to solve a specific human adaptive problem • Hypothesis 2: where males sometimes contribute resources to offspring, females will select males in part based on their ability and willingness to contribute resources CHAPTER 2 page 3  Prediction 1: women have evolved preferences for, and attraction to, men who are high in status  Prediction 2: women have evolved preferences for men who show cues indicating a willingness to invest in them and their children  Prediction 3: Women will divorce men who fail to contribute expected resources if they can do better on the "mating market" • Hypothesis 3: members of the sex that invest less parentally in offspring will be more competitive with each other for mating access to the high-investing sex 1. Theory of Reciprocal Altruism TWO STRATEGIES FOR GENERATING AND TESTING EVOLUTIONARY HYPOTHESES 1. Strategy 1: Theory Driven or "Top-Down" Strategy Going from general to specific • STEP 1 - Derive Hypothesis from existing theory Example: from parental-investment theory, we can derive hypothesis that  because women have a greater obligatory investment in offspring than men, women will tend to me more choosy or discriminating in their selection of a mate • STEP 2 - Test predictions based on hypothesis  Example: conduct an experiment to test the prediction that a woman will impose a longer delay and more stringent standards before consenting to sex to evaluate a man's quality and commitment • STEP 3 - Evaluate whether empirical results confirm predictions  Example: women impose longer delays and impose more stringent standards than men before consenting to sex 1. Strategy 2: Observation-Driven or "Bottom-Up" Strategy Going from specific to general • STEP 1 - Develop hypothesis about adaptive function based on a known observation  Example: A. observation: men seem to give higher priority than women to physical appearance in selection of mate; B. hypothesis: women's physical appearance provided ancestral men with cues to fertility • STEP 2 - Test predictions based on hypothesis  Example: conduct experiments to determine whether men's standards of attractiveness are closely based on cues to woman's fertility • STEP 3 - Evaluate whether empirical results confirm predictions  Example: men find a low wait-to-hip ratio, a known fertility correlate, attractive THE CORE OF HUMAN NATURE: FUNDAMENTALS OF EVOLVED PSYCHOLOGICAL MECHANISMS •All species, including humans, have a nature that can be described and explained CHAPTER 2 page 4 •We provide a definition evoked psychological mechanisms - the core units that compromise human nature •We examine important properties of evolved psychological mechanisms ALL SPECIES HAVE A NATURE •Each species carries its own unique nature - unique adaptations that differ from other species •Ex. It is part of a porcupine's nature to defend itself with quills, the skunk's to defend itself with a spray, and the turtles to defend itself with a shell •Humans also have nature qualities •For Freud human nature qualities consisted of instincts •For Skinner human nature qualities consisted of learning mechanisms DEFINITION OF AN EVOLVED PSYCHOLOGICAL MECHANISM An evolved psychological mechanism is a set of processes inside an organism with the following six properties: 1. An evolved psychological mechanism exists in the form that it does because it solved a specific problem of survival or reproduction recurrently over evolutionary history o This means that the form of the mechanism, its set of design features, is like a key made to fit a particular lock o Just as a shape of key must fit the internal features of a lock o Failure to mesh with the adaptive problem meant failure to pass through the selective sieve of evolution 1. An evolved psychological mechanism is designed to take in only a narrow slice of information o Consider the eye: we can only see a very small array of electromagnetic waves o So the eye is not an all-purpose seeing device, it is designed to process only narrow subsets of information 1. The input of an evolved psychological mechanism tells an organism the particular adaptive problem it is facing o The input lets the organism know which adaptive problem it is dealing with o Ex. The input of seeing a snake, tells you that you are confronting a particular survival problem - physical damage and perhaps death if bitten 1. The input of an evolved psychological mechanism is transformed through decision rules into output o Upon seeing a snake you can decide to attack it or run away from it o The decision rules are a set of procedures for channeling an organism down one path or another o Inputs are transferred through decision rules CHAPTER 2 page 5 o Decision rules are a set of "if, then" statements 1. The output of an evolved psychological mechanism can be physiological activity, information to other psychological mechanisms, or manifest behaviour o Upon seeing a snake you may get physiologically aroused or frightened (physiological output); you may use this information to evaluate your behavioural options such as freezing or fleeing (information to other psychological mechanisms) or you can use this evolution for action, such as running away (behavioural output) 1. The output of an evolved psychological mechanism is directed toward the solution to a specific adaptive problem o Stating that the output of a psychological mechanism leads to solutions to specific adaptive problems does not imply that the solutions will always be optimal or successful o The main point is not that the output of psychological mechanism always leads to a successful solution, but rather that the output of the mechanism on average tends to solve the adaptive problem better than competing strategies in the environment in which it evolved IMPORTANT PROPERTIES OF EVOLVED PSYCHOLOGICAL MECHANISMS A. Evolved psychological mechanisms provide nonarbitrary criteria for "carving the mind at its joints" o The primary nonarbitrary way to identify, describe, and understand psychological mechanisms is to articulate their functions - the specific adaptive problems they were designed by selection to solve o A powerful nonarbitrary analysis of the human mind is one that rests on function o If two components of the mind perform different functions, they can be regarded as separate mechanisms A. Evolved psychological mechanisms tend to be problem specific o Because adaptive problems are specific, their solution tend to be specific as well o Just as general instructions fail to get you to the correct location, general solutions fail to get you to the right adaptive solution o Consider two adaptive problems:  Selecting the right food to eat (a survival problem)  Selecting the right mate with whom to have children (a reproduction problem) o What counts for a successful solution is different for the two problems o We need specific selection criteria - qualities that are part of our selection mechanisms - to solve these selection problems successfully o Problem specificity of adaptive mechanisms tends to be favored over generality because:  General solutions fail to guide the organism to the correct adaptive solutions  Even if they do work, general solutions lead to too many errors and thus are costly to the organism  What constitutes as a "successful solution" differs from problem to problem CHAPTER 2 page 6 A. Humans possess many evolved psychological mechanisms o Because specific problems require specific solutions, numerous specific problems will require numerous specific solutions o Because a large number of different adaptive problems cannot be solved with just a few mechanisms, the human mind must be made up of a large number of evolved psychological mechanisms A. The specificity, complexity, and numerousness of evolved psychological mechanisms give humans behavioural flexibility o With each new mechanism that is added to the mind, an organism can perform a new task o The more mechanisms that we have, the greater the range of behaviours we can perform, and hence the greater the flexibility of our behaviour A.
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